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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="aio.html">

    &project;

  <properties>
    <title>Advanced IO and Tomcat</title>
    <author>Remy Maucherat</author>
  </properties>

<body>

<section name="Table of Contents">
<toc/>
</section>

  <section name="Introduction">

  <p>
    <b>IMPORTANT NOTE: Usage of these features requires using the
    HTTP connectors. The AJP connectors do not support them.</b>
  </p>

  </section>

  <section name="Asynchronous writes">

  <p>
    When using HTTP connectors Tomcat supports using sendfile to send large
    static files. These writes, as soon as the system load increases, will be performed
    asynchronously in the most efficient way. Instead of sending a large response using
    blocking writes, it is possible to write content to a static file, and write it
    using a sendfile code. A caching valve could take advantage of this to cache the
    response data in a file rather than store it in memory. Sendfile support is
    available if the request attribute <code>org.apache.tomcat.sendfile.support</code>
    is set to <code>Boolean.TRUE</code>.
  </p>

  <p>
    Any servlet can instruct Tomcat to perform a sendfile call by setting the appropriate
    request attributes. It is also necessary to correctly set the content length
    for the response. When using sendfile, it is best to ensure that neither the
    request or response have been wrapped, since as the response body will be sent later
    by the connector itself, it cannot be filtered. Other than setting the 3 needed
    request attributes, the servlet should not send any response data, but it may use
    any method which will result in modifying the response header (like setting cookies).
  </p>

  <ul>
  <li><code>org.apache.tomcat.sendfile.filename</code>: Canonical filename of the file which will be sent as
      a String</li>
  <li><code>org.apache.tomcat.sendfile.start</code>: Start offset as a Long</li>
  <li><code>org.apache.tomcat.sendfile.end</code>: End offset as a Long</li>
  </ul>
  <p>
    In addition to setting these parameters it is necessary to set the content-length header.
    Tomcat will not do that for you, since you may have already written data to the output stream.
  </p>

  <p>
    Note that the use of sendfile will disable any compression that Tomcat may
    otherwise have performed on the response.
  </p>

  </section>

</body>
</document>
